The Effect of Dissolved Gasses on the Insulating Properties of Natural Ester and Mineral Insulating Oils

Abstract

This paper presents an investigation into the effect of dissolved gases (DGs) on the insulating properties, such as breakdown strength, of Midel EN 1204 natural ester oil and Poweroil TO 1020 60U mineral oils. The gasses were generated by simulating thermal fault/s at 130 °C, 210 °C, 340 °C, 400 °C, and 450 °C. Dissolved gas analysis (DGA) was conducted according to IEC 60567 to determine the concentrations of H2, CH4, C2H6, C2H4, C2H2, and CO in each of the twelve oil samples. Moisture was measured using the Karl Fischer Method according to IEC 60814. The breakdown voltage (BDV) was measured according to IEC 60156. The results show that total dissolved gas concentration and rate of rise increased with fault temperature in both oils. For this relatively short time experiment, the rise in concentration of DGs had minimal effect. The overall BDV 73.7 kV (virgin ester oil BDV) increased to 76.3 kV at 450 °C for natural ester oil, whereas the BDV of mineral oil decreased from 68.7 kV to 63.1 kV. These findings showed that natural ester oil has better insulation stability under thermal stress.